Pulsed low dose rate brachytherapy for pelvic malignancies

Abstract

The pulsed low dose rate remote afterloading unit was designed to combine the radiation safety and isodose optimization advantages of high dose rate technology with the radiobiologic advantages of continuous low dose rate brachytherapy. This is the first report of a prospective clinical trial evaluating the relative incidence of acute toxicity and local control in patients with pelvic malignancies who underwent interstitial or intracavitary brachytherapy with the pulsed low dose rate remote afterloader. From 5/11/92-6/21/95, 65 patients underwent 77 brachytherapy procedures as part of their treatment regimen for pelvic malignancies. Using the pulsed low dose rate Selectron, equipped with a single cable-driven 0.3-1.0 Ci Ir192 source, target volume doses of 0.40-0.85 Gy per pulse were prescribed to deliver the clinically determined dose. Forty-five intracavitary and 32 interstitial procedures were performed. Fifty-four patients had primary and 11 recurrent disease. Patients were followed closely to assess incidence of Grade 3-5 acute and delayed toxicity, local control, and survival. With a median follow-up of 16.1 months (range 1-29), 33 patients are NED, 10 alive with disease, 13 dead with disease, 4 dead of intercurrent disease, and 5 lost to follow-up. Local control was maintained until last follow-up or death in 48 cases, local failure occurred in 11, unknown in 5. Grade 3-5 acute toxicities (requiring medical or surgical intervention) occurred in 5 out of 77 procedures (6.5%), delayed complications in 10 patients (15% actuarial incidence at 2 years). In the 52 procedures performed for 42 patients with cervix cancer, the acute toxicity incidence was 5.8%, with a 14% 2-year actuarial incidence of delayed complications. Of 32 interstitial templates performed on 30 patients for pelvic malignancies, there were three incidences of acute toxicity and five delayed toxicities. Using the parameters described for this initial clinical study in patients treated for pelvic malignancies, pulsed low dose rate brachytherapy shows no significant increase in acute toxicity above that seen with the standard continuous low dose rate approach. Using the isodose optimization possible with pulsed brachytherapy, local control is excellent in patients treated at initial presentation, although longer follow-up is required for full assessment of local control and late toxicity. Further trials will need to be carried out to determine if larger doses per pulse and shorter total treatment times have comparable therapeutic ratios.